Bump protobuf from 3.12.2 to 3.12.4 (#1230)

Bumps [protobuf](https://github.com/protocolbuffers/protobuf) from 3.12.2 to 3.12.4.
- [Release notes](https://github.com/protocolbuffers/protobuf/releases)
- [Changelog](https://github.com/protocolbuffers/protobuf/blob/master/generate_changelog.py)
- [Commits](https://github.com/protocolbuffers/protobuf/compare/v3.12.2...v3.12.4)

Signed-off-by: dependabot[bot] <support@github.com>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

requirements.txt

@@ -3,7 +3,7 @@ PyYAML==5.3.1
 paho-mqtt==1.5.0
 colorlog==4.2.1
 tornado==6.0.4
-protobuf==3.12.2
+protobuf==3.12.4
 tzlocal==2.1
 pytz==2020.1
 pyserial==3.4